1. Field of Invention
This invention relates to portable self-powered incandescent lighting devices, specifically to improving the ratio of apparent continuous luminous flux emission with respect to wattage of such devices providing illumination, and providing for alternate illuminating and emergency flashing operation of such devices.
2. Description of Prior Art
First and second types of miniature incandescent flashlight bulbs include a filling of krypton gas and a halogen, respectively. The rated or nominal luminous flux emitted by these first two types of bulb is greater than the nominal luminous flux emitted by a third type of miniature incandescent bulb including a tungsten filament and a filling consisting of nitrogen and argon gases. However, the ratio of nominal luminous flux with respect to nominal direct current (DC) wattage of the first and second types, with respect to that of the third type, shows no improvement. Therefore, a portable self-powered lighting device including a bulb of the first or second types as opposed to the third type provides improved intensity of illumination, but also decreased service life of the battery pack of the lighting device.
Supply voltage pulsing circuitry for reducing average wattage of lighting an incandescent lamp without reducing apparent luminous flux emission by the lamp is disclosed by U.S. Pat. No. 4,097,782 to Chambliss (1978). A periodic duty cycle of less than 100% on time is of a minimum time interval allowing the filament of the lamp to momentarily attain the planned or nominal temperature of continuous lighting. Thereby, peak luminous flux emitted by the lamp equals the nominal value of luminous flux emission of the lamp. Where the pulse repetition rate (PRR) of the on- time pulse is equal to about 14. Hertz (HZ), then the human eye perceives overlapping periods of retained images of peak brightness.
It is known that lighting an incandescent lamp by a DC voltage that is greater than the nominal DC voltage of the lamp can result in improvement of the ratio of luminous flux emission with respect to wattage of the lamp, compared to the nominal value of that ratio. A plurality of capacitors charged in parallel and discharged in series can be utilized to obtain a momentary overvoltage for application across first and second electrodes of an incandescent bulb, with the advantage that the voltage of the power supply charging the plurality of capacitors can be considerably less than the voltage of such overvoltage. U.S. Pat. No. 3,824,447 to Kuwabara (1974) discloses such plurality of capacitors wherein false discharging loops of such plurality of capacitors are interrupted by rendering either the source to drain channel of a metal oxide-silicon field effect transistor (MOS FET), or a diode, non-conductive. Where the energy stored by such plurality of capacitors is of a magnitude adequate to light a miniature incandescent lamp, then the MOS FETs of the circuitry for such plurality of capacitors, disclosed by Kuwabara, must be power-type MOS FETs. As a result, interruption of a false discharging loop of circuitry of such plurality of capacitors by rendering the source to drain channel of a power MOS FET as opposed to a diode, non-conductive, is not cost effective.
U.S. Pat. No. 4,835,665 to Kao (1989) discloses an emergency flashlight. The emergency flashlight includes first and second lamps for illumination and emergency flashing, light gathering and focusing elements, and main and auxiliary battery power supplies, respectively. A supply voltage pulsing circuit of the emergency flashlight produces bright bursts of light of the emergency flashing lamp only. The duplication of functional elements providing illumination and emergency flashing by the emergency flashlight, and dedication of the pulsing circuit to the flashing operation of the emergency flashlight only, is inefficient structural design. Also, in most cases, the two functions of the emergency flashlight, of providing illumination and emergency flashing, would be alternately selected.